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Posted on August 16, 2017

PG&E Planning for Potential Effects of Solar Eclipse

By Jennifer Robison

​What’s big and round and blocks the sun?

Yes, your patio umbrella counts. But we’re actually talking about the moon, which will hide the sun in August in a once-in-a-generation solar eclipse that could make things interesting for, well, power generation.

The last total solar eclipse in North America was nearly 40 years ago, in 1979.

But PG&E departments from electric operations to meteorology have been busy analyzing and planning for the eclipse’s potential effects.

“We’ve been coordinating with rest of the Western Interconnection to make sure we’re all on the same page so we can ride through this with minimal customer impact,” said Rod Robinson, senior manager of grid operations. “We’ve been making adjustments to our operations to ensure customer safety and reliability during the eclipse.”

Those adjustments are needed because solar energy has become a vital part of PG&E’s energy portfolio.

The California Independent System Operator, which manages energy flow across 80 percent of the Golden State’s grid, counts nearly 10,000 megawatts of installed solar capacity on a system with a peak load of around 46,000 megawatts. Solar generation across the system hit a record of 9,914 megawatts on June 17.

PG&E’s power portfolio includes 3,833 megawatts of wholesale or utility-scale solar power. What’s more, over 300,000 PG&E customers use private solar. Homes and businesses in PG&E’s service area have installed more than 2,800 megawatts of solar power, and they make up 25 percent of the nation’s households with private solar.

The last total solar eclipse in North America was nearly 40 years ago, in 1979, when California had no solar connected to its grid. That makes it difficult to completely predict how August’s celestial phenomenon will affect the system.

The key risk is that a quick drop in rooftop solar supply could create a sudden spike in demand for traditional generation, ISO officials said.

The eclipse will begin at about 9 a.m. on Monday (Aug. 21) and peak at around 10:15 a.m. in PG&E’s service area. It will reduce the sun’s power by 85 percent in PG&E’s northern region, 75 percent in the Bay Area, and 65 percent along the Central Coast and in Central Valley regions, according to a report by PG&E meteorologist Kevin Clifford.

The eclipse will lead to two concurrent and opposite effects. On one side the eclipse will reduce utility-scale solar supply, which will have to be made up from other energy sources, such as hydroelectric and gas-fired generation. On the other side, the eclipse will reduce the amount of rooftop-solar generation leading to a rise in customer demand. At the eclipse’s peak, Clifford estimates a worst-case scenario of a 2,600-megawatt difference between demand and available energy supply across the PG&E service area. For comparison’s sake, the typical PG&E system load for the late morning of Aug. 21 is 13,500 megawatts, said company meteorologist Scott Strenfel.

The ISO has planned to make up for the loss of as much as 6,000 megawatts of solar generation based on PG&E meteorology estimates compared to an estimated ISO load of 31,100 megawatts in the same time period.

As the solar eclipse moves through PG&E’s service area, non-solar resources will need to ramp up or down to support a system ramping need as much as three times compared to normal conditions.

The rapid swings in demand and supply could tax the grid.

Still, Robinson said he doesn’t anticipate any major problems for PG&E customers.

“We’ve been working to make sure we have the personnel and resources on standby and ready to meet any needs that emerge as a result of the eclipse,” Robinson said.

PG&E will limit routine maintenance work during the eclipse to minimize electric grid impacts, Robinson said.

PG&E’s Energy Policy and Procurement team also is in close coordination with the ISO in preparation for this event.

“We are optimizing generation sources in PG&E’s portfolio to make up any solar shortfall, including planning water levels for hydro watersheds and reservoirs in anticipation for fast-ramping power source needs,” according to Aparna Narang, senior director of electric and gas acquisition.

This is where an active winter storm season should pay dividends. Thanks to heavy rains from October through April, hydro power will be abundant and flexible in August, ISO officials said. That will be key to replacing solar generation lost to the eclipse, and to maintaining grid reliability and stability as the eclipse ends.

Operations leaders are also on top of the possibility that California’s environmental variations —  from raging wildfires to blistering heat storms — could further complicate eclipse response.

“Fires are still a big concern. Operations will be monitoring system conditions so that any proactive steps can be taken to minimize customer impacts,” Robinson said.

Still, in many ways, preparing for the eclipse is like business as usual at PG&E, Robinson said.

“We continuously manage both the potential for incidents affecting the grid and swings in supply and demand on a daily basis,” he said. ISO officials also pointed out that accommodating the eclipse might not be that much different from managing renewable generation on partly cloudy days, which can cause wild swings in solar supply and demand. In some ways, the eclipse will be easier to manage because its timeline and effect on sun power are well-established.

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